Method and apparatus for controlling total dissolved solids in a liquid circulation system

ABSTRACT

A method and apparatus for controlling the total dissolved solids in a liquid circulation system having a sump to which liquid is supplied from a liquid source measures the liquid level in the sump, calculates the average evaporation rate of the liquid over time based on that measurement and also calculates the total dissolved solids level in the liquid based on sump volume, the measured liquid level in the sump, the calculated evaporation rate and the total dissolved solids content of the liquid from the liquid source and adds supply liquid to the liquid circulating system when the calculated total dissolved solids content in the liquid in the system attains a predetermined level.

BACKGROUND OF THE INVENTION

The present invention relates to controlling the level of totaldissolved solids in liquid circulation systems such as direct forceddraft evaporative coolers and closed loop cooling towers or the like.

DESCRIPTION OF THE PRIOR ART

Conventional types of industrial cooling towers include so-calledcounterflow towers wherein water or other liquid falls or is sprayeddownward in the tower counterflow to air moving upwardly in the tower inthe opposite direction. Such systems are used for a variety ofapplications including water air scrubbers, dust collection equipment,air cooling towers, evaporative coolers, fluid coolers or closed loopcooling towers, evaporative condensers or the like. Typically suchindustrial cooling towers are quite large and permanent.

Some relatively small towers for such purposes have been built which aretransportable for various applications such as roof towers. These aredisclosed, for example, in U.S. Pat. Nos. 5,227,095; 5,487,531; and5,545,356. Another improved system is disclosed in PCT/US2010/024929(Feb. 22, 2010); Publication WO 2010/110980, the disclosure of which isincorporated herein by reference.

Historically, such cooling towers and other devices described above,both opened and closed, have been made of metal components which areprone to corrosion, fouling, and scaling of the heat transfer surfacesas a result of the dissolved solids in the liquid being circulated. Suchcorrosion, fouling or scaling affects the efficiency and operation ofthese systems. Many attempts have been made to overcome these problems,but few have been successfully implemented. Such attempts include theuse of chemical additives, systems for bleeding and replenishing theliquid used in the circulation system based on measurements of makeupflow, CA ions in the liquid, conductivity of the liquid, and measurementof the ratio of the concentration of chloride ions versus calcium todetermine if calcium is plating on or off of the metal surface of thesystem.

For example, U.S. Patent Publication No. US 2005/0036903 discloses theuse of a so-called Peutt Analyzer to sample, periodically orcontinuously, the presence of calcium ions in the makeup water and thecooling tower water, performing a series of calculations based on thatdata to establish a measurement of calcium ion behavior in the water andusing those calculations to increase or decrease chemical treatmentand/or increase or decrease bleed-off rates from the cooling tower. Thusthis device appears to be actually measuring the dissolved solids or ascale producing chemical.

U.S. Pat. Nos. 3,754,741; 3,805,880; 4,361,522; 5,213,694; and 6,740,231each disclose variants on what is referred to as a “feed and bleedsystem”. Basically, these systems measure the water level in the systemand supply makeup water as needed, along with chemical treatment.

U.S. Pat. No. 5,013,488 discloses measuring the density of the water inan evaporative cooling system to selectively discharge suspended solidsand replace the discharge water with fresh water containing additives.

U.S. Pat. No. 6,510,368 discloses a process for measuring performancecharacteristics, including corrosion measurements, in order to controlthe supply of makeup water and appropriate chemicals.

Japanese Patent Application Publication JP 63243695 uses measurements oftower performance, i.e., water temperature in, water temperature out,and flow rate to calculate an evaporation rate which in turn is used todetermine how much water to add and/or bleed. Thus, this system isdependent on simply the proportion of liquid consumed in order to supplyreplacement liquid.

All of these systems are relatively complex and expensive.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a simple and inexpensivemethod and apparatus for controlling the total dissolved solids in aliquid circulation system.

Another object of the invention is to control total dissolved solidswith a system that enables the performance of diagnostics on systemperformance.

Another object of the invention is to replace liquid in a liquidcirculating system to control dissolved solids based on calculating thedissolved solid contents in the system over time.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, a method andapparatus for controlling the total dissolved solids in a liquidcirculation system such as open or closed loop cooling towers or thelike is disclosed. The invention is not limited to such systems, but issuitable for any type of system in which a liquid is circulated and cancontaminate or affect the efficiency of the system as a result of thepresence of dissolved solids which can precipitate within the systemand/or produce scale. The system is connected to a liquid supply whichhas a known measured, or estimated, total dissolved contents and whichis used to replenish liquid in the system. In operation, the method andapparatus measures the liquid level in a sump of the system, at leastperiodically over time, and calculates, again at least periodically overtime, the average liquid evaporation rate based on the liquid levelmeasurements. This evaporation rate is then used to calculate the totaldissolved solids level in the liquid based on the sump volume, themeasured or calculated solids level in the sump, the calculatedevaporation rate, and the total dissolved solids content of the supplyliquid. In response to that calculation, the sump is partially drainedand supply liquid is added to the liquid circulation system when thecalculated total dissolved solids content attains a predetermined level.Upon the addition of supply liquid, the system recalculates the totaldissolved solids content in the liquid recirculating system based on thequantity of supply liquid added. These steps are repeated over timeduring the operation of the system. The sump is replenished periodicallyto replace the evaporated water, and the calculated tank total dissolvedsolids is corrected based on the sump volume, the measured or calculatedsolids level in the sump, the amount of water added, and the totaldissolved solids content of the supply liquid.

The method and apparatus of the present invention is especially designedfor use in liquid circulating systems that are formed primarily ofpolymeric components, although the invention is not limited to the useof such components. In systems having polymeric components, heatexchangers may be composed of small polymeric tube bundles, for example,rather than metallic tubes, finned or unfinned. The advantages ofsystems of that type is that the polymeric tube bundles have the abilityto shed scale build-up based on dissolved solids. Such scale build-up isthe leading cause of cooling efficiency deterioration in cooling towers.As a result, in such polymeric tube systems, some scaling can bepermitted and therefore the need for precise measurement of dissolvedsolids or conductivity, as is attempted in the prior art, is notnecessary. Applicant has found that computational methods for thedetermination of total dissolved contents based on sump conditions isuseful.

In addition, the system of the present invention allows for thedetermination of chemical and biological component treatment of theliquid in the system. Thus, the feed rate of such chemical treatment andbiological agents can be controlled by the system as well.

With regard to biological growth, it has been found that many of thebiocides that are candidates for use in cooling towers or the like usingpolymeric materials are not compatible with many of the polymers,including nylon. These biocides include bromines, chlorines, and ozone.Accordingly it has been found that the addition of fresh water withbatch replenishment, rather than continual replenishment, has theadditional advantage of “shocking” the sump with the chlorine residualin municipal supplies and thus contains biological growth.

The above and other objects, features and advantages of this inventionwill be apparent to those skilled in the art from the following detaileddescription of illustrative embodiments thereof, when read inconjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of an exemplary direct forced draft/fluidcooler for which the method and apparatus of the present invention isadapted;

FIG. 2 is a side elevational view of the system shown in FIG. 1, withthe side wall removed;

FIG. 3 is a schematic illustration of the system and apparatus of theinvention;

FIG. 4 is a view similar to FIG. 3 of another embodiment thereof; and

FIG. 5 is a view similar to FIG. 3 of yet another embodiment thereof;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in detail, and initially to FIG. 1, adirect draft fluid cooler 10 is illustrated. The cooler is designed toadvantageously use the evaporation of water or other liquids to cool asecond liquid in a heat exchanger located within the device. Suchsystems can be used with water or other suitable liquids and althoughthe illustrative embodiments are described as utilizing water, theinvention is not limited to the use of water or to a direct draft fluidcooler liquid circulation system. It is the intent that the invention isapplicable to all types of liquid fluid circulation systems which may besubjected to deterioration as a result of total dissolved solids and/orscale.

The fluid cooler 10 includes an exterior housing 12 having a top 14,vertical side walls 15, end walls 17, and a bottom wall 16. As seen inFIG. 2, wherein the side wall 15 has been removed to illustrate theinterior of the device, housing 12 also contains a liquid distributionsystem 20 at its upper end and a heat exchanger 24 which is illustratedin the drawing as a cooling coil type structure. This cooling coil andthe other components of the liquid distribution system may be made ofpolymeric materials such as nylon as described above. The coil is formedof curved piping having an inlet end 26 for supplying a liquid to becooled to the heat exchanger and an outlet 28 for supplying the cooledliquid (for example glycol) to an outside system, e.g. a refrigerationsystem.

A water collector 30 is located within the housing 12 beneath the heatexchanger coil 24 for collecting the evaporative cooling water thatpasses through the spaces between the coil system from the waterdistribution system 20. One or more fans are provided in the bottom ofthe housing 12, supported therein in any convenient manner, for drawingair through the bottom opening of the housing and blowing it through thewater collector 30 (which has a structure as described inPCT/US2010/024929 (Feb. 22, 2010); Publication WO 2010/110980, thedisclosure of which is incorporated herein by reference) and the coolingcoil 24 countercurrent to the water distributed from the distributionsystem 20.

Water distribution system 20 further includes a collection tank or sump34 mounted outside housing 10 at the approximate level of the fans toreceive the water collected by the collection system 30. The collectedwater is discharged from the tank 34 through a discharge pipe 36 to apump 38. The pump recirculates the liquid through the distribution pipe40 to which a plurality of nozzles 42 are connected. These nozzles,which are located within the housing, as seen in FIG. 2, create adownward spray of water above the heat exchange coil 24. These nozzlesmay be of known construction suitable for use in fluid coolers orevaporative cooling devices.

In the type of system disclosed in FIG. 2, over time, total dissolvedsolids in the liquid flowing in the liquid distribution or circulationsystem 20 can form scale, film or other deposits on the piping of theheat exchanger 28 or in the collector 30. Some of this material willflake off of the polymer and ultimately collect in the tank or sump 34.

The system and apparatus for controlling the amount of dissolved solidsin the system, in order to minimize scale build-up and to periodicallyremove precipitated dissolved solids from the sump, is shown in FIG. 3.That illustration depicts the device of FIG. 1 schematically, and thereference numerals therein that are identical to those in FIGS. 1 and 2represent the same parts.

The control system illustrated in FIG. 3 includes a controller 40, whichconsists of a microprocessor adapted to receive information from sensorsin the system and either alone or by inputting signals to a computer orthe like, performs certain calculations used to control fluid flowvalves in response to the calculations. More specifically, the systemincludes liquid supplied to the system through the valve 42 into thesump 34. The liquid is supplied from a known source 44, e.g., the publicwater supply system, and contains either a known total dissolved solidscontent (which is publicly available information from the municipality)or a total dissolved solids content which has been determined by priortesting in any conventional manner. The valve 42 is controlled by thecontroller 40, as described hereinafter, to periodically supply freshliquid to the sump.

A second valve 46 is connected to the drain line 48 of sump 34. Thisdrain valve is also responsive to the controller 40 based oncalculations made in the controller or an associated computer. Thestructure and control of these valves 42, 46 is well known in the art,and need not be described herein in detail.

The system illustrated in FIG. 3 further includes a means 50 fordetermining the liquid level in the sump 34. That sump is of knowndimensions and volume. These dimensions and volume are input by theoperator into the memory of the controller 40, in any conventionalmanner, to perform the calculations described hereinafter. The sensormeans 50 can be a conventional float valve, or a pressure sensor in thebottom of the sump which determines the level of the water in the sumpbased on the pressure measured at the sump bottom. These sensors providea signal to controller 40 representative of the liquid level in thesump. This signal can be monitored continuously or at leastperiodically, over time, to allow the controller to make the requiredcalculations. When the circulating pump is running an additional amountof liquid is contained in the tower or housing 12 as “holdback” volume.This volume is known and can be measured, and when the pumps are runningthis additional volume is added to the measured sump volume forcalculations of total dissolved solids.

In operation, the level of the liquid in the sump 34 is continuouslymeasured by the sensor means 50. The information about the level of thewater in the sump is provided to the controller which continuously (orperiodically) calculates the average evaporation rate over time and usesthat calculation to in turn calculate the dissolved solids level in theliquid in the sump.

The average evaporation rate is a simple mathematical calculation overtime. The entire system, when the sump is filled, contains a knownvolume of liquid and as the liquid evaporates, the level in the sumpdecreases. With the volume of the sump being known, along with the totalvolume of the liquid the system can hold, calculation of the evaporationrate is a simple mathematical process. Knowing the rate of evaporation,and the total dissolved solids of the liquid originally supplied to thesystem, the controller can compute the amount of total dissolved solidsin the liquid in the sump over time based on the evaporation rate. Thatis, the liquid supplied from the line 44 has a known total dissolvedsolids (tds) content in terms of parts per million by volume. Since thetdss do not evaporate, by determining how much liquid has evaporatedover time, it is a simple calculation to determine how many ppms oftotal dissolved solids remain in the system after it has been operatingfor a period of time. Thus, for example, if 50% of the liquid in thesystem evaporates, the originally known tds ppm in the system hasdoubled after a 50% evaporation rate.

In order to control the amount and rate of build-up of scale in thesystem, the controller will activate drain valve 46 to drain sump waterwhich has reached the maximum tds allowed. After this partial drain thecontroller will activate the valve 42 to supply additional liquid to thesystem as necessary to keep the total dissolved solids content in theliquid below a predetermined level, for example, below 400 ppm. Thecontroller also opens fill valve 42 as needed to replenish evaporatedwater and maintain the tank level between minimum and maximum levels.

The controller monitors the fill valve to determine how much liquid isadded to the system, and uses that information to recalculate the tds inthe system, continuously adding liquid to the system as needed. However,as liquid is replenished to the system, the tds will increase in thesystem over time. When the tds achieve a predetermined level, the systemmust be purged. Thus, when that predetermined level of tds in the sumpis achieved, the controller operates the drain valve 46 to expel liquidfrom the system. Since, in the preferred embodiment, the materials ofwhich the cooling tower are made include a substantial amount ofpolymers, scale which flakes off from the polymeric material willcollect in the sump, settle to the bottom and be discharged from thesystem. Upon dumping a predetermined amount of liquid from the sump, thecontroller closes the drain valve and refills the sump, recalculates thetds in the system based on the amount of liquid discharged from the sumpwith its tds content, and begins the process over again.

This system, as illustrated in FIG. 3, additionally allows the operatorto monitor the efficiency of the operation of the system by calculatingthe cooling accomplished by the evaporative load 24. This is done by asimple formula in which the calculated evaporation rate is multiplied bythe heat of evaporation of the liquid (which is a known factor). Whenthe efficiency decreases below the desired level, the system can be shutdown for cleaning

In another embodiment, illustrated in FIG. 4, the controller 40 is usedto perform diagnostics on the performance of the system. In thisembodiment, a sensor 60, located adjacent the air discharge at the upperend of the housing 12, which measures the leaving air enthalpy (i.e.,the enthalpy of the air that leaves the cooling tower or housing 12) andprovides a signal representative of the measured leaving air enthalpy tothe controller. Another, similar sensor 62 is provided to measure theambient air enthalpy and provides a signal representative of themeasured ambient air temperature to the controller. These signals areused by the controller to determine the air side cooling performance ofthe system By comparing the air side cooling performance of the towerbased on these measurements with the water side cooling performancecalculated by the controller, the controller can provide informationabout how the measured operation compares to predicted performance.

FIG. 5 illustrates another embodiment of the invention wherein themeasured feed rate of water by the controller is used to calculate theamount of chemical or biocide treatment which is to be provided by asupply 70 to the sump 34. The controller 40 operates the valve 72 todispense a predetermined amount of chemical or biocide to the systembased on the amount of liquid being replenished in the system inresponse to the sensor 50 and actuation of fill valve 42. Alternatively,the controller can use the calculated total dissolved solids and themeasured feed water to determine the chemical feed rates.

Although the invention has been described herein with reference to thespecific embodiments shown in the drawings, it is to be understood thatthe invention is not limited to such precise embodiments and thatvarious changes and modifications may be effected therein withoutdeparting from the scope or spirit of the invention.

What is claimed is:
 1. A method for controlling the total dissolvedsolids in a liquid circulation system using a liquid supply having aknown, measured, or estimated total dissolved solids content andincluding a sump, said method comprising the steps of; a) measuring theliquid level in the sump at least periodically over time; b) calculatingat least periodically the average liquid evaporation rate over timebased on the liquid level measurements; c) calculating at leastperiodically the total dissolved solids level in the liquid based on thesump volume, the measured calculated liquid level in the sump, theevaporation rate and the total dissolved solids content of the supplyliquid; d) draining a portion of the sump volume when the calculated tdsreaches a predetermined limit; e) adding supply liquid to the liquidcirculation system to replenish the sump volume and reduce the tds andto maintain the sump level between maximum and minimum levels; f)recalculating the totals dissolved solids content in the liquidcirculatory system after the addition of supply liquid based on thequantity of supply liquid added; and g) repeating steps a) through e)over time during operation of the system.
 2. The method as defined inclaim 1 wherein steps a); b) and c) are performed continuously.
 3. Themethod as defined in claim 1 or claim 2 wherein the step of measuringthe liquid level is performed using a liquid level sensor.
 4. The methodas defined in claim 3 wherein said liquid level sensor is a pressuretransducer.
 5. The method as defined in claim 1 or claim 2 wherein theliquid circulation system is an evaporative cooling system and themethod includes the step of calculating the cooling load performance ofthe evaporative cooling system based on the calculated evaporation rateand the heat of evaporation of the liquid.
 6. The method as defined inclaim 5 including the step of comparing the calculated cooling loadperformance with the predicted air side cooling performances of theevaporative cooler based on the values of the enthalpy of thesurrounding ambient air and the enthalpy of the air leaving theevaporative cooler.
 7. The method as defined in claim 6 including thestep of measuring the enthalpy of the ambient air and leaving air. 8.The method as defined in claim 1 or claim 2 including the step ofmeasuring the amount of liquid supplied to the system in step e) andsupplying at least one liquid treatment chemical to the liquidcirculating system based on that measurement.
 9. The method as definedin claim 1 or claim 2 including the step of measuring the amount ofliquid supplied to the system in step e) and using that measurement andthe content calculated total dissolved solids to supply liquid chemicaltreatment to the liquid in the system.
 10. The method as defined inclaim 1 or claim 2 including the step of periodically draining the sumpnear its bottom to flush precipitated solids there from.
 11. A liquidcirculation system connected to a source of liquid for circulationtherein, in which total dissolved solids in the liquid circulating inthe system is controlled, said system comprising: a) a liquidcirculation path in the system including a sump for liquid; b) means formeasuring the liquid level in the sump, at least periodically, while thesystem is in operation; c) controller means for calculating, at leastperiodically the average evaporation rate over time based on the liquidmeasurements in the sump; and for calculating the total dissolved solidslevel in the liquid based on the sump volume, the liquid level in thesump, the calculated average evaporation rates and the total dissolvedsolids content of the supply liquid; d) means responsive to saidcontroller for draining of portion of the sump volume when thecalculated total dissolved solids reaches a predetermined level e) meansresponsive to said controller for supplying liquid from said liquidsource to the system in order to reduce the level of total dissolvedsolids and to maintain sump levels between predetermine minimum andmaximum levels; and e) said controller being adapted to recalculate thetotal dissolved solids content in the liquid circulating in the systemafter the addition of liquid to the system based on the quantity ofliquid added and the total dissolved content calculated before theliquid additive.
 12. The system as defined in claim 11 wherein saidmeans for measuring the liquid level in the sump is a liquid levelsensor.
 13. The system as defined in claim 11 wherein said means formeasuring the liquid level in the sump is a pressure transducer.
 14. Thesystem as defined in claim 11 wherein said liquid circulation systemincludes an evaporative cooling section and said controller means isadapted to calculate the cooling load performance of the evaporativecooling section based on the calculated liquid evaporation rate and theheat of evaporation of the liquid.
 15. The system as defined in claim 14wherein said controller means is adapted to compare the calculatedcooling load performances of the evaporative cooling section with thepredicted air side cooling performance of the evaporative cooler sectionbased on the values of the enthalpy of the surrounding ambient air andthe enthalpy of the air leaving the evaporative cooler section.
 16. Thesystem as defined in claim 14 including means for measuring the enthalpyof the ambient air and for measuring the enthalpy of the air leaving theevaporative cooler.
 17. The system as defined in claim 11 includingmeans for measuring the amount of liquid supplied to the system inresponse to the calculated total dissolved solids content of the liquidand supplying at least one liquid treatment chemical to the liquidcirculating system based on that measurement.
 18. The system as definedin claim 11 including means for measuring the amount of liquid suppliedto the system in response to the calculated total dissolved solidscontent and for using that measurement and the calculated totaldissolved solids content to supply liquid chemical treatment to theliquid in the system.
 19. The system as defined in claim 11 includingmeans responsive to said controller for periodically draining the sumpnear its bottom to flush precipitated solids therefrom.
 20. The systemas defined in claim 13 wherein said means for draining the sump isresponsive to the controller means calculation of a total dissolvedsolids content in the liquid that is higher than the total dissolvedsolids content at which liquid is added to the system.
 21. The system asdefined in claim 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 wherein saidmeans for measuring the liquid level in the sump operates continuouslyand said controller continuously calculates the average evaporation rateand total dissolved solids level of the liquid.
 22. A method forcontrolling the total dissolved solids in a liquid circulation systemusing a liquid supply having a known measured or estimated totaldissolved solids content and including a sump, said method comprisingthe steps of; a) measuring the liquid level in the sump at leastperiodically over time; b) calculating at least periodically the averageliquid evaporation rate over time based on the liquid levelmeasurements; c) calculating at least periodically the total dissolvedsolids level in the liquid based on the sump volume, the measuredcalculated liquid level in the sump, the evaporation rate and the totaldissolved solids content of the supply liquid; d) draining a portion ofthe sump periodically when the calculated tds reaches a predeterminedlimit; and e) adding supply liquid to the liquid circulation system tomaintain a predetermined liquid level in the sump and reduce sump tds.23. A liquid circulation system connected to a source of liquid forcirculation therein, in which total dissolved solids in the liquidcirculating in the system is controlled, said system comprising: a) aliquid circulation path in the system including a sump for liquid; b)means for measuring the liquid level in the sump, at least periodically,while the system is in operation; c) controller means for calculating,at least periodically the average evaporation rate over time based onthe liquid measurements in the sump; and for calculating the totaldissolved solids level in the liquid based on the sump volume, theliquid level in the sump, the calculated average evaporation rates andthe total dissolved solids content of the supply liquid; and d) meansresponsive to controller to partially drain sump when the calculated tdsreaches a predetermined level; and e) means responsive to saidcontroller for supplying liquid from said liquid source to the systemwhen the calculated total dissolved solids content attains apredetermined level.